Dredge is a graveyard mechanic that can replace a card draw by milling a specified number of cards and returning the card with dredge from your graveyard to your hand. Repeated dredging can move huge portions of a library into the graveyard.
Cards such as Narcomoeba, Prized Amalgam, and Creeping Chill turn being milled into an advantage, allowing Dredge decks to build a battlefield or pressure life totals without conventionally drawing and casting every card.